1. Field of the Invention
The invention relates to a reservoir for powdery media, in particular for powder coating, having: (a) a housing having at least one inlet and at least one outlet for the powdery medium; (b) a fluidising floor of porous, air-permeable material arranged in the interior of the housing at a distance from its base; and (c) a pressure chamber chargeable with compressed air and located between the fluidising floor and the base of the housing.
2. Background Art
In the powder processing industry, in particular in coating technology, reservoirs for powdery media in which a given quantity of powdery medium can be temporarily stored and then withdrawn for further use are often required. Such reservoirs are to be found, for example, upstream of, downstream of or in sifting machines which are provided upstream of the application devices with which the powder coating is sprayed onto a workpiece in coating plants. The amount of sieved powder coating required for complete coating of a workpiece is generally collected in reservoirs located downstream of the sifting machine.
Known reservoirs of the above-mentioned type currently on the market have substantially cylindrical housings; the term “cylindrical” is used here in the mathematical sense to describe a geometrical form which has the same cross-section at all levels above its base. Suction pipes which are lowered from above into the interior of the housing until they are relatively close to the upper face of the fluidising floor, from where they suck the fluidised powdery medium upwardly, are used as outlets.
With the known reservoirs of the above-mentioned type there is a danger that the powdery medium withdrawn therefrom will not possess the same distribution of grain sizes as the powdery medium located inside the reservoir, so that a particular fraction of grains, whether a coarser or finer fraction, is preferentially withdrawn, depending on where the intake aperture of the suction pipe happens to be located.
Moreover, these known reservoirs have a considerable consumption of compressed air. The fluidised powdery medium located in them is also subjected to high mechanical stress, which can lead to undesired fine-grain formation. Furthermore, mixing of the fluidised powder is not always optimal. Finally, in these known reservoirs unwanted air can occasionally be sucked in through the outlet pipe from the generally pulsating fluidised bed of powder, interrupting the operation of the application devices in a manner referred to as “pumping”.
It is the object of the present invention so to configure a reservoir of the above-mentioned type that the grain size distribution in the powdery medium withdrawn does not differ substantially from the grain size distribution of the powdery medium inside the reservoir, and that the grain size distribution therein remains substantially constant over time.